Field of the Invention
The invention relates to a device for continuously fractionating a gas by adsorption, a method for continuous adsorption fractionation with processor-controlled testing of an operating capability of an adsorption drier system, and a device having an in-service testing device in a processor-controlled adsorption drier system in which regeneration is performed by a flow of regeneration gas.
Adsorption fractionation is used in particular when drying compressed air. Compressed air is the energy medium used in production processes. Modern production methods and processing operations are placing ever higher demands on the requirements for compressed air. These days, it is no longer sufficient to provide a specified quantity of compressed air since the compressed air must also conform to specified purity criteria. That being the case, the need to be able to produce dry, clean compressed air has assumed a certain amount of importance. In the case of adsorption fractionation, water molecules from the air tend to adhere to an adsorbent.
A device for adsorption fractionation is described, for example, in a document entitled "Trockene Druckluft. Mit Sicherheit ein reiner Gewinn", published by Ultrafilter GmbH, Bussingstra.beta.e, D-42781 Haan, Germany, and in an English language version entitled "Dry Compressed Air The Cleanest Solution--Guaranteed" published by Ultrafilter International. The German language document is known by reference T.997.004.03.D 10.95 and the English language document is known by reference T 997.005 03 GB/D 6/96. With that device, it is possible to dry compressed air on a continuous basis. To that end, the device has two containers filled with adsorbent. When the device is operating, moist air is circulated through one of the containers, where it is dried accordingly, while some of the dried air is simultaneously fed into the other container where the adsorbent is regenerated in a direction opposite that of the flow, i.e. it picks up water molecules from the adsorbent. The air which is moistened again in that way is expanded during regeneration and discharged to the ambient environment.
Another device used for adsorption fractionation with gases is described in European Patent Application 0 168 336 A2, corresponding to U.S. Pat. No. 4,631,073. That publication contains a wealth of information giving details of the adsorption technique and some relating to process control.
The set-up costs for building such devices represent a considerable proportion of the costs involved. Accordingly, they will depend on the cost of the number of individual components to be assembled and the cost of manufacturing them. Furthermore, additional costs are also incurred if in-service testing has to be conducted on the device through the use of a function monitoring system. The components needed for that purpose also have to be mounted on the system, which means that the number of components will essentially depend on the type of in-service testing being used. Various techniques used for that purpose are known from the prior art, some more complex than others, and are configured to meet certain safety specifications.
A sampling device is known from U.S. Pat. No. 4,127,395, through the use of which a moisture sensor can be tested for operating capability. If an indicator shows that the moisture sensor has failed, the adsorption drier system can be automatically switched to time-controlled operation. Operation of that sampling device requires several additional lines to be run to the adsorption drier system. Another device is disclosed in U.S. Pat. No. 4,504,286, along with a method for controlling the switching function between two containers of adsorbent, whereby switching still continues even if the actual moisture monitoring function fails. That is a processor-controlled system which compares the maximum storage capacity of a bed of adsorbent with the time integer of the water flowing through it. A moisture analyzer is used in conjunction with other components to measure the proportion of water being circulated.
In practice, it has often been found while maintenance work is being carried out on supposed disruptions in the adsorption drier system, that it is necessary to check if the regeneration air is being discharged from alternating sides, either acoustically or by observing two manometers mounted on the containers for the adsorbents. Possible sources of failure in that area are the shuttle valves, discharge valves and overflow passages for regeneration air. However, it is not possible to give a more accurate plant-related diagnosis of the fault or even the source of the fault, particularly in older adsorption drier systems. Consequently, because of the type of testing, suspected disruptions in the adsorption drier plant are not further investigated unless there has already been a perceptible degradation in the quality of the compressed air being delivered.